This invention relates to high speed testing of high density display panel arrays, and more particularly to a method and apparatus for performing tests of high density panels such as LCD (Liquid Crystal Device) panels, using electro-optic assisted and non-contact methodologies.
LCD panels use either an active matrix panel technology or direct multiplex panel technology. Active matrix panels include an active component associated with each pixel enabling retainment of the pixel state after a refresh operation. As a result, contrast and flicker problems are minimized. Accordingly, active matrix panels are well-suited for large displays. Direct multiplex panels include relatively simple circuitry which enable dense pixel populations, but are subject to flicker in large arrays.
Referring to FIG. 1, a typical active matrix LCD panel segment 10 is shown consisting of an array of pixels 12. Each pixel 12 is activated by addressing simultaneously an appropriate drive line 14 and gate line 16. A drive element 18 is associated with each pixel. The drive lines 14, gate lines 16, pixels 12 and pixel drive elements 18 are deposited on a clear glass substrate by a lithographic or similar process. Because of the high pixel densities, the close proximity of the gate lines and drive lines, and the complexity of forming the pixel drive elements (i.e. FET transistors), there is a significant probability of defects occurring during the manufacturing process.
Known testing methods for high density LCD panels include contact testing methodologies which require connection to and testing of each individual row/column intersection within the panel array. Advanced probing technology is necessary to establish reliable contacts among the densely populated pixel elements. Such test methods are time-consuming and prone to error. For an LCD array of 640 by 480 pixel elements, a typical test cycle requires approximately 300,000 connections and consumes about two hours. The time and expense of testing, although necessary, is a limiting factor to the commercial success of large array LCD panels. A faster and more efficient testing method is needed to reduce the testing costs, and thereby reduce the product costs of LCD panels so as to compete with CRT and other display types.
Accordingly, it is desireable to be able to test large arrays easily, without direct individual electrical connection and with connections only as needed.